The influence of elevated glucocorticoid levels and exposure to stressful experiences on adult neurogenesis raises the question of what is the functional impact of changing the rate of new neuron production in the adult hippocampus. Since the hippocampus is important for certain types of learning and memory (Moser et al., 1993; Ergorul & Eichenbaum, 2004), anxiety regulation (Bannerman et al., 2004) and shutting off the HPA axis (Herman et al., 1989; Jacobson & Sapolsky, 1991; Herman et al., 1995; Herman & Mueller, 2006), these present possible functions that may be affected by changes in adult neurogenesis. It should be emphasized at the outset of this discussion, that stress and glucocorticoids exert effects elsewhere in the hippocampus, including on the pyramidal cell population (Fig. 2). These effects, which include changes in the biochemistry, electrophysiology and structure of neurons in the CA fields, are likely to contribute to stress-induced changes in hippocampal function. The extent to which changes in adult neurogenesis, through the connections of the granule cell population to other neuronal populations (e.g., CA3 pyramidal neurons, hilar mossy cells), participate in
